1. Field of the Invention
The present invention relates to an image forming apparatus such as a digital copying machine, and to an image forming method, for reading an image on a color original by image reading means such as a color scanner, processing the read image data, and forming an image by means of a printer.
2. Description of the Related Art
In the prior art, input image data is subjected to a filtering process to control the degree of sharpness.
When the sharpness is controlled and it is desired to vary the degree of sharpness among plural areas such as character areas/photo areas, this desire can be satisfied by adopting a structure permitting setting of the degree of sharpness in the respective areas.
However, when arithmetic operations for the filtering process are performed, an arithmetic error, such as cancellation of significant digits, may occur depending on the precision (bit number) of an arithmetic circuit and a decimal point position of the arithmetic result.
For example, when a difference is large between a maximum absolute-value coefficient and a minimum absolute-value coefficient in a group of coefficients constituting the filter, an arithmetic result may be rounded down because it is too small relative to the precision of the arithmetic circuit.